(1) Field of the Invention
The present invention relates to an audio output apparatus and a television broadcast receiver.
(2) Description of the Related Art
In a conventional electronic apparatus such as a television broadcast receiver provided with an audio output apparatus, a muting operation of the audio circuit has been executed by a personal computer. FIG. 4 shows a schematic block diagram of a conventional audio output apparatus and FIG. 5 shows a timing chart indicating timing of the muting operation executed in the conventional audio output apparatus.
Referring to FIG. 4, the conventional audio output apparatus 5 is substantially made up of a supply circuit 1, audio circuit 2, microcomputer 3, and protect circuit 4.
The supply circuit 1 receives a supply voltage from an external commercial power supply or the like and generates various voltages based on the supply voltage to supply the voltages to respective components such as the supply circuit 1, audio circuit 2, and microcomputer 3 of the audio output apparatus 5. The audio circuit 2 receives an audio signal, applies predetermined audio processing to the audio signal, and outputs the resultant signal to a speaker or the like (not shown).
The microcomputer 3 is electrically connected with each of the components forming the audio output apparatus 5. The CPU as an internal component of the microcomputer 3 controls the entirety of the audio output apparatus 5 in accordance with programs written in the ROM and RAM also being the internal components of the microcomputer 3.
The protect circuit 4 monitors the output voltage of the supply circuit 1 and outputs a protect signal to the microcomputer 3 when an abnormal increase or decrease in the output voltage occurs. The microcomputer 3, upon receipt of the protect signal, outputs a mute signal to the audio circuit 2 to cause the audio circuit 2 to stop outputting of the audio signal to the speaker or the like.
Operations performed in the audio output apparatus 5 during the period from when the power supply voltage to the supply circuit 1 is stopped to when the outputting of the audio signal from the audio circuit 2 is stopped will be described with reference to the timing chart of FIG. 5. When the power supply to the supply circuit 1 is stopped on account of removal of the AC cord as shown in the drawing, for example, the supply voltage output from the supply circuit 1 gradually decreases and hence the protect circuit 4 detects the decrease and outputs a protect signal.
Upon receipt of the protect signal, the microcomputer 3 generates a mute signal for muting the audio circuit 2 and outputs it to the audio circuit 2. Since, upon receipt of the mute signal, the audio circuit 2 stops outputting of the audio signal, even if the voltage supply from the power supply circuit then becomes deficient so as to generate an audio signal to cause an audio noise (pop sound), the audio signal to cause the audio noise is not output from the audio circuit 2 to the speaker or the like.
Configurations similar to the above apparatus that is controlled by a microcomputer so as to mute the audio signal when the supply of power voltage has been abruptly stopped are disclosed in Japanese Unexamined Patent Application Publication Nos. H4-220093, S63-236485, and H4-217818.
When the conventional method as described above was carried out, however, it sometimes occurred that the power supply from the supply circuit 1 to the audio circuit 2 became deficient before the microcomputer 3 output the mute signal. Therefore, sometimes the audio circuit 2 was turned off before the mute signal from the microcomputer 3 arrived at the audio circuit 2. Hence, there was a possibility that an audio noise was output to the speaker or the like.